Increased C02 from climate change puts clownfish in peril

MARK COLVIN: Australian biologists are warning that global warming could be the end of the clownfish.

The orange and white fish was made famous by the movie Finding Nemo.

But it could be hard to find clownfish in the future because increasing levels of carbon dioxide are turning the fish into risk takers that are attracted to their predators.

Felicity Ogilvie reports

FELICITY OGILVIE: Australian Scientists decided to test what life will be like for clownfish if carbon dioxide levels continue to rise.

A hundred baby fish were caught, and put into tanks with higher carbon levels - those expected in the ocean by the end of the century.

Then they released the clownfish back onto the Great Barrier Reef at Lizard Island.

MARK MEEKAN: It's a very scary world out there for a little fish when it first arrives on the reef and lots and lots of mouths out there are ready to eat them.

FELICITY OGILVIE: Mark Meekan is from the Australian Institute of Marine Science.

MARK MEEKAN: So normally little fish are very, very shy. They're not very bold. They hang inside the coral and they're very wary.

Now, once we subjected these little fish to excess carbon dioxide, basically they lost that caution, that natural caution that they should have had. They started wandering out from the coral, became much bolder and as a result, much more vulnerable to predators.

FELICITY OGILVIE: Not only did the clownfish take risks by swimming off the reef many swam straight towards their predators.

That's because higher levels of carbon dioxide affect the clownfish's sense of smell.

MARK MEEKAN: Normally the fish would smell a predator and go away from it. Unfortunately the effect of the carbon dioxide was to muck up that sensory system so that in some cases they were even attracted to predators.

FELICITY OGILVIE: Do you know why the carbon dioxide is affecting the fish's sense of smell?

MARK MEEKAN: Look we don't really know what exactly is going on with the sensory system of the fish but clearly it's having a pretty bad effect.

It's not a great idea if you're a baby fish to swim towards your predator. Why the fish are actually doing that we can't say for certain but we certainly can say that the carbon dioxide isn't having any good effects on their sensory systems.

FELICITY OGILVIE: But it's not all bad news for the clownfish.

The team tested the fish at various carbon dioxide levels. At the lower levels half of the fish were still able to smell their predators.

But after just a small increase of carbon, all of the baby fish were attracted to their predators.

The lead researcher is Professor Philip Munday from James Cook University in Townsville.

PHILIP MUNDAY: One of the most important things that we noticed was that about 700 parts to the million of CO2 - this is a level that we might see towards the second half of the century - that there was some individual variation. Some individuals seemed to be more tolerant of the CO2 than others and that suggests that there might be some capacity for adaptation.

However at higher levels, at around about 850 parts per million, we saw no individual variation. That suggestions there's no capacity for adaptation at that higher level.

FELICITY OGILVIE: And what levels are expected by the end of the century?

PHILIP MUNDAY: If we don't get serious about controlling greenhouse gas emissions the IPCC predict that the levels could be around about 850 parts per million by the end of the century.

FELICITY OGILVIE: The team will now try to work out if other fish will be affected in the same way as the clown fish.

The scientists say all fish share the same sensory system so it's assumed they all have their sense of smell altered by climate change.